May is the time to finalise all the spring planting, as the increased heat boosts all plants to really take off.
From now until November one key to success is to water deeply but appropriately for each plant.
It is now ideal to plant tropical plants of all kinds, including citrus and other tropical fruit and flowering trees, palms, and flowering vines such as bougainvillea.
Tropicals like being planted during their active growing season and April and May serve well, but act early to avoid the potential of a spell of scorching heat. Planting now means they can establish themselves during the summer and harden off in winter. Feed and water them through spring and summer.
Potted roses can still be transplanted into your garden in May. Continue to monitor for and act against pests and diseases.
When temperatures are mild with cooler or damper evening air, mildew can become a threat. Continue to water (twice a week now) and fertiliser (once a month with a proprietary feed). Prune by picking or deadheading.
Continue to feed citrus and avocado trees, water lilies, azaleas and camellias after bloom, fuchsias, sweet corn, peppers when flowers first show, flowerbeds, lawns.
Succulents, cacti and euphorbias
Fertilise all container-growing succulents with well diluted complete liquid fertiliser. Water them only if the soil is dry 2 cm below the surface.
Prune winter and spring-flowering vines, bushes, trees and ground covers when they have finished flowering. Osteospermum appreciates a cut early in the month after bloom as this prevents a buildup of thatch; another flush of bloom will follow. Lightly cutting back winter-flowering jasmine will produce a second show; after that cut it back hard, almost to bare wood, to prevent tangled interior growth and to enable it to produce new wood for blooms next year.
Leptospermum can be shaped by cutting in bloom to be used for cut flowers; once blooming is over, whole unwanted branches can be cut out and tips of selected branches headed back to increase bushiness. Wisteria, once established and the size you want, can have any unwanted growth cut back to two or three buds from the main branch.
Continue to keep spring-flowering bulbs well watered. A dose of liquid fertiliser after blooming will help give bulbs extra strength for next year’s flowering. Cut off their leaves only after they have gone brown.
Annuals and Perennials
May is a good time to replace cool-season flowers which will have peaked in April. Pull out the ones which have finished or nearly finished blooming, clean up the beds and add some fertiliser, and replant with summer annuals. If you started some off from seed, they can be transplanted now.
But if you have not, there is no shortage of choice from local garden centres, such as cosmos, marigolds, petunias, and verbena for full sun and begonias, impatiens, and lobelia for partial shade. There are many, many others, of course. When planting out from a container, remember to loosen the plants’ roots.
In May it is finally time to plant those real heat-lovers, such as zinnias, from seed. Morning Glory seeds can go in now, but need to be nicked or they won’t sprout. Grasp the seed with some pliers and use a small file to scarify the edge of the seed; then soak overnight in warm water before planting.
For planting most seeds, dig the ground and work in some compost and fertiliser. Rake the area smooth and sprinkle seeds on the top. With the back of a hoe, press down lightly on the seeds. Some seeds need light in order to germinate, so don’t cover those types with soil. Keep the area damp until the plants get established.
At the same time, some plants will need deadheading or cutting back this month.
Although it is too late to plant the cool-season grasses from seed, others such as Bermuda should be planted in May. Lawns can be planted from seeds, plugs grown in flats, some can be from creeping stems with roots attached or it can arrive as turf. No matter what type is to be used, it is important that the ground below it is properly prepared. When decided on which type, take advice from local gardeners and garden centres.
Continue to feed warm-season grass, but stop feeding cool-season grass. Continue to mow and water all lawns.
Watering is the most important task as vegetables will be growing fast now. The drip irrigation system uses the least water.
If any vegetables show signs of slowing down, apply vegetable fertiliser to the side of the row and water in. Be careful not to overfertilise beans or tomatoes with nitrogen which will result in a proliferation of leaves but without much fruit.
Continue to plant for continuous crops. Staggering plantings should result in longer harvests. All the vegetables can be put in now, including beets, carrots, corn, cucumbers, eggplant, green beans, melons, some spinach, peppers, pumpkins, radishes, summer squash, tomatoes and many herbs.
Harvest the vegetables once they are ready as this encourages new ones to grow, rather like deadheading flowers. Most crops are better harvested young and tender. Continue to tie up tomatoes on stakes and pinch out suckers to maintain one or two main trunks per plant.
Keep the soil evenly moist in order to avoid blossom-end rot.
Pick herbs to keep them in bounds and plant more. Although there is little research about the impact of herb crops on vegetable crops, many gardeners feel that interplanting promotes a more pest-free environment.
Last year’s parsley will probably have already gone to seed, so best to pull it all up now and plant a new rows in another spot. If you leave a few plants behind, however, to go to seed, the flowers will attract beneficial insects.